An electroluminescing arrangement (EL arrangement) is characterised in that when an electrical voltage is applied it emits light accompanied by a flow of current. Such arrangements have been known for a long time under the description “light-emitting diodes”) (LEDs). The emission of light is due to the fact that positive charges (“holes”) and negative charges (“electrons”) recombine with the emission of light.
The LEDs conventionally used in technology all consist to a very large extent of inorganic semiconductor materials. For some years however EL arrangements have been known whose basic constituents are organic materials.
These organic EL arrangements generally contain one or more layers of organic charge transport compounds.
The principal layer structure of an EL arrangement is as follows:    1 Carrier, substrate    2 Base electrode    3 Hole-injecting layer    4 Hole-transporting layer    5 Emitter layer    6 Electron-transporting layer    7 Electron-injecting layer    8 Top electrode    9 Contacts    10 Coating, encapsulation
This structure represents the most detailed case and may be simplified by omitting individual layers, so that one layer assumes several tasks. In the simplest case an EL arrangement consists of two electrodes between which is arranged an organic layer that fulfils all functions, including the emission of light.
It has been found in practice however that in order to enhance the light-emitting diode electron-injecting and/or hole-injecting layers in the electroluminescing assemblies are particularly advantageous.
From EP-A 686 662 it is known to use special mixtures of conducting organic polymeric conductors such as poly(3,4-ethylenedioxythiophene) and for example polyhydroxy compounds or lactams as electrode in electroluminescent displays. It has been found in practice however that these electrodes do not have a sufficient conductivity, especially for large area displays. The conductivity is however sufficient for small displays (luminous area <1 cm2).
From DE-A 196 27 071 it is known to use polymeric organic conductors, for example poly(3,4-ethylenedioxythiophene), as hole-injecting layers. The luminosity of the electroluminescing displays can thereby be significantly increased compared to structures that do not employ polymeric organic intermediate layers. The conductivity can be specifically adjusted by reducing the particle size of the poly(3,4-alkylenedioxythiophene) dispersions. In this way it is possible to prevent electrical crosstalk between adjacent address lines, especially in passive matrix displays (EP-A 1 227 529).
The service life of these displays is however still not sufficient for many practical applications.
There therefore existed the need to produce EL arrangements that have, in addition to a high luminosity (luminous intensity), a longer service life, in particular a longer service life at a high luminosity, than known EL arrangements.